WASHINGTON, Sept 5 (Reuters) - U.S. President Donald Trump accused social media companies of interfering with the upcoming congressional elections, without appearing to offer any evidence, in an interview published on Wednesday ahead of congressional testimonies from top social media executives.

Referring to companies such as Facebook Inc and Twitter Inc, Trump, a Republican, told the Daily Caller in an interview conducted on Tuesday "I think they already have" interfered in the Nov. 6 election.

The report gave no other details.

Trump's accusation added to recent charges he and Republican lawmakers have made of political bias against conservatives by social media companies and search engines.

"The true interference in the last election was that — if you look at all, virtually all of those companies are super liberal companies in favor of Hillary Clinton," he said, referring to his Democratic opponent in the 2016 presidential election.